The invention relates to an arithmetic element for processing digital input increment signals, the frequency of which indicates an analog quantity, notably digital input increment signals comprising a sign signal according to the DDA (digital differential analyser) principle, comprising at least one arithmetic device for executing add and subtract operations, and at least one operand register which is connected to a data input of the arithmetic device.
Arithmetic elements of this kind are known, for example, from U.S. Pat. No. 3,035,768 and from the book "The Digital Differential Analyser", T. R. H. Sizer, ed. Chapman & Hall, London, 1968, notably pages 11 to 27. The DDA technique was developed to enable replacement of, for example, pure analog arithmetic elements. This technique utilizes so-called increment signals. These signals are often ternary signals which in practice consist of two separate but associated binary signals, that is to say a value signal and a sign signal which together describe the three states +1, 0, -1. The value of an analog signal is proportional to a pulse frequency of the value signal; this is also referred to as a "frequency-analog signal". The associated sign signal indicates the polarity. When such a pulse frequency is applied to an up/down counter whose counting direction is determined by the sign signal, the value pulses are algebraically summed in accordance with the sign. Thus, an integration is achieved, the result thereof being present in the counter as a binary number. Similarly, other known analog arithmetic elements can be realized by digital means.
Like in the analog technique, known arithmetic elements based on the DDA principle and constructed for different functions also require devices of different construction. This implies very high costs of manufacturing and storage. Furthermore, the digital components available thus far reach processing speeds which are not necessary for most applications of the DDA principle, so that part of their capacity remains unused. Finally, the cost of digital components is generally higher than that of analog components. The advantages of the digital technique, notably the higher accuracy, are then accompanied by comparatively high costs.